Flow Parameter

FlgurĀ» 8.19 (Continued> The latest version of the GPDC pressure drop correlation, (c) The Kister and Gill GPDC (SP) chart for structured packings only.

hanced frothiness may also be explained by a switch from a vapor- to a liquid-continuous dispersion, which, according to Billet and Schultes (78,79), takes place at a flow parameter of 0.4. It is worth noting that the prediction difficulty at higher flow parameters is not unique to the Eckert correlation, but has also been noticed in other correlations (736,78,79).

For nonaqueous systems, the Eckert correlation is also optimistic for flow parameters lower than 0.03, which are typical of vacuum distillation and/or low liquid rates. Robbins (89) shows that the GPDC correlation use of liquid density and liquid viscosity is invalid at low flow parameters, where liquid properties should have little effect on pressure drop. It is worth noting that according to Robbins, this prediction difficulty is not unique to the Eckert correlation, but will be encountered whenever a correlation predicts a pressure drop dependence on liquid properties at low liquid rates.

Predictions from the Eckert correlation are sensitive to the packing factor (Sec. 8.2.10). Strigle (15) and Kister and Gill (60) found that most packing factors reported in the literature are satisfactory. However, for a few packings, the packing factors gave poor fit to experi-

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